LHSE Presents Introduction to Chemistry Temperature Conversions Previous lecture Math for Chemistry Temperature Heat Temperature 3 Temperature scales (F o, C o, K) Equations for converting between scale Algebra with conversion equations Examples
Heat The components of matter (atoms and compounds) are in constant motion This includes those in solid objects. Motion is energy Motion energy is Heat More motion means more Heat Most substance expand with more motion (Heat) Temperature Temperature is NOT: Motion Heat Temperature IS: a MEASUREMENT of the amount of Heat Often measured using a thermometer (Heat meter)
Thermometer Thermometers are filled with a liquid (mercury) that expands when heated Thermometers have a scale (to gauge the height of the liquid) The scale is divided into equal parts, called degrees ( ) There are 3 common scales Fahrenheit Celsius (centigrade) They measure the same height but give different numerical values Like a ruler in inches and centimeters Temperature scales Fahrenheit, an older scale (1724) in which water freezes at 32 F and boils at 212 F Mainly used in the US; Scale HAS negative numbers Celsius is the modern scale in which water freezes at 0 C and boils at 100 C There are 100 between the temperature of freezing & boiling (that is how the scale was constructed) Scale HAS negative numbers is the absolute scale of temperature. The lowest possible temperature is 0 K (no sign) Water freezes at 273.15 K and boils at 373.15 K There are 100 between the temperature of freezing & boiling Scale HAS NO negative numbers
Fahrenheit Celsius 71.5 F o 22 C o 295.15K Same height different number of steps -32 F o 0 C o 273.15K Same height different degrees Formulas for Converting Temperatures Since each scale is reading the same temperature converting between scales doesn t alter the true value for the amount of heat Convert Fahrenheit to Celsius Fahrenheit Fahrenheit = 9/5 * (Celsius) + 32 = Celsius + 273.15 Celsius = - 273.15
Examples Convert Fahrenheit to Celsius The average temperature of the human body is 98.6 o F. What is it in Celsius? Celsius = 5/9 * (98.6 32) Celsius = 5/9 * (66.6) = (5*66.6) /9 Celsius = 333/9 Celsius = 37 o C Fahrenheit Fahrenheit = 9/5 * (Celsius) + 32 When the thermometer reads 40 o C. What is the temperature in Fahrenheit? Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit = 9/5 * (40) + 32 Fahrenheit = (360) /5 + 32 Fahrenheit = 72 + 32 Fahrenheit = 104 o F = (9* 40) /5 + 32
= Celsius + 273.15 Dry ice turns to gas at -78.5 o C. What is the temperature in? = Celsius + 273.1 = -78.5 + 273.1 = 194.6 K = Celsius + 273.15 A balloon rising in the sky cooled the helium within to 281? What is it in Celsius? = Celsius + 273-273 -273-273 = Celsius 281-273 = Celsius 8 = Celsius
Algebra and Conversion Formula Solve for Celsius 5 9 5 C + 32 32 = F 32 ( 9 5 C ) = 5 ( 9 9 F 32 ) 5 C = ( F 32 ) 9 Remove the 32 Remove the 9/5 ( ) 9 5 C = 9 F 32 5 9 5 9 5 9 5 Solve for Fahrenheit C = ( F 32 ) + 32 + 32 C +32 = F Remove the 5/9 Remove the -32
Examples II The instruction on a pizza box says to bake at 425 F. What temperature is needed on the Celsius scale? What about on the scale? Convert Fahrenheit to Celsius Celsius = 5/9 * (425 32) Celsius = 5/9 * (393) = (5*393) /9 Celsius = 1965/9 Celsius = 218.3 o C Examples II The instruction on a pizza box says to bake at 425 F. What temperature is needed on the Celsius scale? What about on the scale? = Celsius + 273.15 Convert Fahrenheit to Celsius Celsius = 218.3 o C = Celsius + 273.1 = 218.3 + 273.1 = 491.4 K
Examples II The temperature on the moon can get to 400. What is the same temperature on the Celsius scale? What about on the Fahrenheit scale? = Celsius + 273.15 = Celsius + 273-273 = Celsius 400-273 = Celsius 123 o C = Celsius Examples II The temperature on the moon can get to 400. What is the same temperature on the Celsius scale? What about on the Fahrenheit scale? = Celsius + 273.15 Fahrenheit Fahrenheit = 9/5 * (Celsius) + 32 123 o C = Celsius Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit = 9/5 * (123) + 32 Fahrenheit = (1107) /5 + 32 Fahrenheit = 221.4 + 32 Fahrenheit = 253.4 o F = (9* 123) /5 + 32
RECAP Atoms and compounds are in constant motion Motion energy is Heat (atomic scale) Temperature IS a MEASUREMENT of the amount of Heat Thermometers have a scale (to gauge the height of the liquid) There are 3 common scales Fahrenheit (water freezes at 32 F and boils at 212 F) Celsius (water freezes at 0 C and boils at 100 C) (The lowest possible temperature is 0 K (no sign)) They measure the same height /different numerical values There are Formulas for Converting between Temperatures scales Fahrenheit = 9/5 * (Celsius) + 32 = Celsius + 273.15 Practice!